GSM roaming question

[Mikhail Umorin]

Hello --

I cannot access network in certain locations (in Texas, USA) on my FR using 
ATT SIM card. However, when I use the same SIM in the ATT GoPhone that came 
with the card, I have access to a network. "Operators" button in the phone 
settings in SHR-U shows only "Automatic" and "T-Mobile".

So, is this roaming problem a bug? misconfiguration? not implemented? not 
possible?